Process of manufacturing nitrites and nitrates.



H. PAULING. PROCESS OF MANUFACTURING NITR ITES AND' NITBATBS. APPLICATION FILED APR. 9, 1910.

991,356; Patented May 2, 1911.

WITNESSES S r INVENTOR M m- S x 1 fi lforneyS UNITED STATES PATENT OFFICE.

HARRY PAULING, or enLsENxracnnN, GERMANY, assroNon-ro satrnrnnsliunn INDUSTRIE-GESELLSCHAFT, e. M. B. 11., or enrsnnxmcnnn, GERMANY.

rnocnss or manorao'rnam'e 'm'rn'rrns m nrrmrns.

Specification of Letters Patent.

rammed May 2, 1911.

Application filed April 9, 1910. Serial No. 554,617.

T c all whom it may concern:

Be it known that I, HARRY PAULING, subject of the King of Saxony, residing'at 84 Wilhelmstrasse, Gelsenkirchen, in the Kingdom of Prussia, Empire of Germany, have invented a new and useful Improvement in Processes of Manufacturing Nitrites and Nitrates; andI do hereby declarethe following to be a full, clear, and exact descrip" tion-of the same.

This invention relates to processes-of recovering nitrates and nitrites; and it com first treatment .of the nitrous gases; all as more fully hereinafter set forth and as claimed.

. In the absorption of nitrous gases, such as for example are produced by the oxidation of atmospheric nitrogen, by solutions of alkalis and alkaline earths, by carbonates, etc.,it is well known that where such gases are not too concentrated, a mixture of nitrates and nitrites is produced, the propor tion of nitrite's increasing with the dilution of the gases. This absorption by alkalis is often utilized in the arts, sodium carbonatebeing the absorbent generally used. With sodium carbonate the valuable salt sodium nitrite may be easily produced, but in prac tice it is diflicult to separate this nitrite from the less valuable sodlum nitrate formed at the same time. The nitriteand nitrate are of approximately the same solubility in water and other solvents, whether hot or cold, so that by evaporation and concentration, 'or' by limited solution,- only the excess of one'salt or the other can-be obtained in a comparatively pure state. With a mixture of 80 parts nitrite and parts nitrate, only .60 parts at most of nitrite ran be easily obtained-in anisolated state, the remaining 20 parts of nitrite remaining admixed with the 20 partsof nitrate. This mixture is of'comparatively small value as compared with either of its components in a pure state; and

particularly with nitrite.

In the absorption it is usual to employ the countercurrent principle, the nitrous. ga es being passed successively through a serie oftowers while the absorbent liquid or lye flows throu h the series in the other direct-ion. In this manner of operation obviously the gas mixture which has gone through several absorption towers and contains but lit-.

tle oxidized nitrogen comes into contact with the freshestand strongest lye/while the nearly saturated lye or solution comes into contact with fresh gases. The proportion of sodium carbonate in the lye decreases as it passes onward until in the last tower (the first as regards gas) the carbonate is practically all eliminated and the solution becomes one of nitrate and nitrite. Nitric 'iieidvapors areabsorbed at all points by the manner. For this purpose, absorption is conducted in a series of towers. These towers are all traversed by the gases to be treated, such gasespassing from one to another in the usual manner. The absorbent liquid does not however flow directly through the whole series as in the ordinary practice. Instead, the first tower in series (as regards gases) is supplied with a special absorbent liquid whilethe soda solution or other ab- It is the object of the present invention to conduct the operationin a more methodical-- sorbent liquid is transmitted through the i remaining towers in a direction opposed to the flow of gases but is'intercepted at the base of the second tower in series (as regards gases). This absorbent lye is removed at original carbonate mainly] oh wholly re} placed by nitrogen acids, and is mainly or wholly a solution of nitrate and nitrite. This solution is evaporated and crystallized to obtain sodium nitrite and a mother liquor containing both nitrate and nitrite in ap proximately equal amounts. This mother liquid is used as the absorbent liquid in the this point with the carbon dioxid of the sively and rapidly diluted thereby that further oxidation does not take place to any extent, and the gases leaving the tower are adapted to produce mainly nitrite by. the further absorption treatment with alkali. When the liquor in the first tower in series becomes acid and is no longer capable of absorbing, it is spent and contains mainly or wholly nitrate, which can be separated by evaporation and crystallization, the residual mother liquor being returned to the tower. Operating in this manner, the percentage of nitrite produced in the second and subsequent towers-is much higher than usual.

The accompanying drawing shows diagrammatically an arrangement of apparatus elements suitable forcarrying out the process of the present invention, the course of the .liquid through the various towers and vats being indicated by direction arrows.

The alkaline liquid, for example a 20 per cent. sodium carbonate solution, flows through towers V, IV,- III, and II, meeting and absorbing nitrous gases flowing in the opposite direction. The liquor issuing from tower II and containing dissolved matter of which, say, about 85 per cent. is nitrite and about 15 per cent. is nitrate, passes as indicated by 2 into an evaporatingmpparat-us 7 for concentration. The concentrated liquor is led into crystallizing tanks 9 where sodium nitrite crystallizes out, leaving a residual mother liquor containing about equal parts of sodium nitrite and sodium nitrate in' solution, together with a small amount of sodium carbonate. This mother liquor; is then conducted as at 4 to tower l where it meets the fresh nitrous gases from which it absorbs substantially all the nitric acid. In this absorption the sodium carbonate remaining in the mother liquor is decomposed and the nitrite is changed to nitrate with evolution of nitrous gases. These evolved nitrous gases are so diluted by the large volume of unabsorbed gases passing through and leaving tower I, that i therei! practically no opportunity for them to become oxidized; and consequently the quantity of nitrates formed in the succeeding towers is much less than usual.

The li nor 5 leavingtower I is free of nitrite an contains practically only nitrate. It may be concentrated in evaporator8, and

pure nitrate maybe crystallized out-"at 10,-

the residual mother lye being returned if de sired to tower I as by pipe 6, shown dotted.

The specific proportions given in the fore-' going example vary of course with varying condltions of operation. ,1

To summarize briefly: In the ordinary method of operation a series of consecutively placed towers are employed. In these the grses are washed by an alkali solution on t e countercurrent' principle, the operation sidual carbonate, as in the ordinary practice.

the nitric acid decomposes nitrite, yielding nitrate and evolving nitrous vapors which pass forward with the residual nitrous -vapors into the first tower of the regular series where absorption by carbonate solution is effected, with the production of a solution high in nitrites.

What I claim is 1. The process of manufacturing nitrate and nitrite, which comprises absorbing nitrous gases in lye, separating nitrite from said lye, causing fresh nitrous gases to act trate produced thereby.

2. The process of manufacturing nitrate and nitrite which comprises absorbing .nitrous gases in lye, separating nitrite from said lye by evaporation and crystallization, causing fresh nitrous gases to act on the residua-l lye,'and separating-the nitrate produced thereby.

3. The process of manufacturing nitrate and nitrite which comprises absorbing nitrous in lye, separating nitrite from said lye, causing fresh nitrous gases to act successively on the residual lye and .on a fresh body of lye, and separating the nitrate produced thereby in said residual'lye.

on the residual lye, and separating the ni- 4. The process of manufacturing nitrate and nitrite which'comprises passing nitrous gases throu h a series of towers, passing lye in the opposlterdirection through part of said series, separating nitrite from the lye which has traversed this part of said series, passing the residual lye through'the, remainder of said series, an separating nitrate from said residual lye after the passage of the latter through the remainder ofsaid series.

5; In the manufacture of nitrite and nitrate, the processwhich comprises treating gases containing nitrogen oxids with a Sub stantially neutral solution containing nitrite and anitrate, and then treating the unabsorbed and the evolved gases with an alkaline solution.

6. In the manufacture of nitrite and ni-- trate, the process which comprises passing an alkaline liquid against a counter-currentof preliminarily treated nitrous gases until said liquid is nearly neutral, separating nitrite from the resulting liquid, and preliminarily treatin nitrous gases with the mother trhte, the process which comprises passing 1i nor from t e nitrite separation. gases containing nitrogen oxids through a 1:, In the manufacture of nitrite and nitower supplied with a substantiallymeutral trate, the process which comprises passing solution of nitrite and nitrate, and'then'passa solution of sodium carbonate against a ing the unabsorbed and the evolved gases counter-current of nitrous gases to obtain a through towers fed wlth an alkaline solution.

liquor containing nitrite and nitrate, with- In testimony whereof, I have signed my 29 drawing such liquor from the said current name to this specification in the presence of of gases and separating out part of said nitwo subscribing witnesses.

trite; and treatin) fresh nitrous gases with HARRY PAULING.

the resulting mot er liquor to absorb nitric \Vitnesses: acid. ABRAHAM ScHLEsmeuR,

8. In the manufacture of nitrite and ni- LoUIs MUELLER. 

